Lets invent JAYSON :D

   (dog){
      "ears": [(ear){"side": "right"}, (ear){"side": "left"}]
      {% this is a comment %}
   }

Now we only have to invent attributes, and we can sell this XML skin to the enterprise JSON users.

(This is only half sarcasm)

EDIT: Even Better, make comments a subtree by having a special type tag, like #. this way, (#,dog){...} can stay in the tree, but is ignored.